.\"	$OpenBSD: setuid.2,v 1.23 2014/09/09 08:16:12 jmc Exp $
.\"	$NetBSD: setuid.2,v 1.3 1995/02/27 12:37:06 cgd Exp $
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.\"     @(#)setuid.2	8.1 (Berkeley) 6/4/93
.\"
.Dd $Mdocdate: September 9 2014 $
.Dt SETUID 2
.Os
.Sh NAME
.Nm setuid ,
.Nm seteuid ,
.Nm setgid ,
.Nm setegid
.Nd set user and group ID
.Sh SYNOPSIS
.In unistd.h
.Ft int
.Fn setuid "uid_t uid"
.Ft int
.Fn seteuid "uid_t euid"
.Ft int
.Fn setgid "gid_t gid"
.Ft int
.Fn setegid "gid_t egid"
.Sh DESCRIPTION
The
.Fn setuid
function sets the real and effective user IDs and the saved set-user-ID
of the current process to the specified value.
The
.Fn setuid
function is permitted if the effective user ID is that of the superuser,
or if the specified user ID is the same as the effective user ID.
If not, but the specified user ID is the same as the real user ID,
.Fn setuid
will set the effective user ID to the real user ID.
.Pp
The
.Fn setgid
function sets the real and effective group IDs and the saved set-group-ID
of the current process to the specified value.
The
.Fn setgid
function is permitted if the effective user ID is that of the superuser,
or if the specified group ID is the same as the effective group ID.
If not, but the specified group ID is the same as the real group ID,
.Fn setgid
will set the effective group ID to the real group ID.
Supplementary group IDs remain unchanged.
.Pp
The
.Fn seteuid
function
.Pq Fn setegid
sets the effective user ID (group ID) of the current process.
The effective user ID may be set to the value
of the real user ID or the saved set-user-ID (see
.Xr intro 2
and
.Xr execve 2 ) ;
in this way, the effective user ID of a set-user-ID executable
may be toggled by switching to the real user ID, then re-enabled
by reverting to the set-user-ID value.
Similarly, the effective group ID may be set to the value
of the real group ID or the saved set-group-ID.
.Sh RETURN VALUES
.Rv -std setuid seteuid setgid setegid
.Sh ERRORS
.Fn setuid
and
.Fn seteuid
will succeed unless:
.Bl -tag -width Er
.It Bq Er EPERM
The user is not the superuser and the requested
.Fa uid
or
.Fa euid
is not the process's real, effective, or saved UID.
.El
.Pp
.Fn setgid
and
.Fn setegid
will succeed unless:
.Bl -tag -width Er
.It Bq Er EPERM
The user is not the superuser and the requested
.Fa gid
or
.Fa egid
is not the process's real, effective, or saved GID.
.El
.Sh SEE ALSO
.Xr getgid 2 ,
.Xr getuid 2 ,
.Xr issetugid 2 ,
.Xr setgroups 2 ,
.Xr setregid 2 ,
.Xr setresgid 2 ,
.Xr setresuid 2 ,
.Xr setreuid 2
.Sh STANDARDS
The
.Fn setuid ,
.Fn seteuid ,
.Fn setgid ,
and
.Fn setegid
functions conform to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn setuid
system call first appeared in
.At v1 ;
.Fn setgid
in
.At v4 ;
and
.Fn seteuid
and
.Fn setegid
in
.Bx 4.2 .
